fix: install.sh Mac Intel compatibility + Studio no-torch support (#4624)

* fix: install.sh Mac Intel compatibility + Studio no-torch support (#4621)

On Intel Macs (x86_64), PyTorch has no wheels for torch >= 2.3, so the
installer crashes. Even when torch is absent, Studio crashes on startup
because two files have bare top-level torch imports.

Studio's GGUF inference (llama.cpp) does not need PyTorch. Training and
HF-inference already isolate torch to subprocesses. Only 2 files in the
server startup chain had top-level torch imports preventing startup.

Changes:
- install.sh: detect architecture, default to Python 3.12 on Intel Mac,
  skip torch install, add Python 3.13.8 guard for arm64, pass
  UNSLOTH_NO_TORCH env var to setup.sh
- data_collators.py: remove unused `import torch` (no torch.* refs)
- chat_templates.py: lazy-import IterableDataset into function bodies
- install_python_stack.py: add IS_MACOS/NO_TORCH constants, skip
  torch-dependent packages, skip overrides.txt, skip triton on macOS

No existing working flow changes. Linux/WSL and macOS arm64 behavior is
identical.

* tests: add test suite for Mac Intel compat + no-torch mode

Shell tests (test_mac_intel_compat.sh):
- version_ge edge cases (9 tests)
- Architecture detection for Darwin x86_64/arm64, Linux x86_64/aarch64
- get_torch_index_url returns cpu on simulated Darwin
- UNSLOTH_NO_TORCH propagation to both setup.sh branches

Python unit tests (test_no_torch_filtering.py):
- _filter_requirements with NO_TORCH_SKIP_PACKAGES
- NO_TORCH env var parsing (true/1/TRUE/false/0/unset)
- IS_MACOS constant check
- Overrides skip and triton macOS skip guards

Python import tests (test_studio_import_no_torch.py):
- data_collators.py loads in isolated no-torch venv
- chat_templates.py has no top-level torch imports
- Negative control confirms import torch fails without torch

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* tests: add E2E sandbox tests for Mac Intel no-torch mode

Replace static/synthetic test stubs with real sandbox tests:

- Shell: E2E uv venv creation at Python 3.12, mock uv shim to verify
  torch install is skipped when MAC_INTEL=true, dynamic env propagation
  test for UNSLOTH_NO_TORCH in both local and non-local install paths
- Python filtering: test real extras.txt and extras-no-deps.txt with
  NO_TORCH_SKIP_PACKAGES, subprocess mock of install_python_stack() for
  5 platform configs (NO_TORCH+macOS, Windows+NO_TORCH, normal Linux,
  Windows-only, macOS-only), VCS URL and env marker edge cases
- Python imports: parametrized Python 3.12+3.13 venv fixture, dataclass
  instantiation for all 3 collator classes, chat_templates.py exec with
  stubs, negative controls proving import torch and torchao install fail
  in no-torch venvs

91 total tests, all passing.

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* fix: address reviewer findings for Intel Mac no-torch mode

P1 fixes:
- Auto-infer NO_TORCH in install_python_stack.py via platform.machine()
  so `unsloth studio update` preserves GGUF-only mode without needing
  the UNSLOTH_NO_TORCH env var (6/10 reviewers)
- Add openai-whisper and transformers-cfg to NO_TORCH_SKIP_PACKAGES
  since both have unconditional torch dependencies (4/10 reviewers)
- Skip unsloth-zoo on Intel Mac --local installs (depends on torch)
  in both migrated and fresh install paths (1/10)
- Recreate stale 3.13 venvs as 3.12 on Intel Mac re-runs (1/10)
- Detect Apple Silicon under Rosetta via sysctl hw.optional.arm64
  and warn user to use native arm64 terminal (1/10)

P2 fixes:
- Wire new test files into tests/run_all.sh (4/10 reviewers)
- Add update-path tests (skip_base=False) for Intel Mac
- Add _infer_no_torch tests for platform auto-detection

P3 fixes:
- Fix macOS progress bar total (triton step skipped but was counted)
- Fix temp file leak when Windows + NO_TORCH filters stack

All tests pass: 30 shell, 66 Python (96 total).

* feat: add --python override flag to install.sh

Lets users force a specific Python version, e.g. ./install.sh --python 3.12.
Addresses M2 Mac users whose systems resolve to a problematic 3.13.x patch.
When --python is set, the Intel Mac stale-venv guard and 3.13.8 auto-downgrade
are skipped so the user's choice is respected.

* tests: add comprehensive E2E sandbox tests for no-torch mode

Add test_e2e_no_torch_sandbox.py with 7 test groups (43 tests total)
covering the full no-torch import chain, edge cases, and install logic:

- Group 1: BEFORE vs AFTER import chain comparison (proves the bug
  existed and the fix works by synthetically prepending top-level torch
  imports)
- Group 2: Dataclass instantiation without torch
- Group 3: Edge cases with broken/fake torch modules on sys.path
- Group 4: Hardware detection fallback to CPU without torch
- Group 5: install.sh flag parsing, version resolution, arch detection
- Group 6: install_python_stack.py NO_TORCH filtering
- Group 7: Live server startup without torch (marked @server, skipped
  when studio venv is unavailable)

All 43 tests pass on both Python 3.12 and 3.13 isolated venvs.

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* feat: add --no-torch flag to install.sh/ps1, fix lazy import bug in dataset formatting

- Fix chat_templates.py: narrow torch IterableDataset import into inner
  try/except ImportError so dataset.map() works without torch installed
- Fix format_conversion.py: same lazy import fix for convert_chatml_to_alpaca
  and convert_alpaca_to_chatml
- Add --no-torch flag to install.sh with unified SKIP_TORCH variable
  (driven by --no-torch flag OR MAC_INTEL auto-detection)
- Add --no-torch flag to install.ps1 with $SkipTorch variable
- Print CPU hint when no GPU detected and --no-torch not set
- Replace MAC_INTEL guards with SKIP_TORCH in torch install sections
- Update shell tests (40 pass) and Python tests (90 pass)

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* fix: address reviewer findings for --no-torch installer paths

- Fix migrated-env branch in install.sh and install.ps1: check
  SKIP_TORCH first, then branch on STUDIO_LOCAL_INSTALL. Previously
  SKIP_TORCH+non-local fell into else and installed unsloth-zoo (which
  depends on torch), defeating --no-torch mode.
- Fix $env:UNSLOTH_NO_TORCH leak in install.ps1: always set to "true"
  or "false" instead of only setting on the true branch. Prevents stale
  no-torch state from leaking across runs in the same PS session.
- Fix install_python_stack.py update path: add NO_TORCH guard around
  base.txt install so unsloth studio update does not reinstall
  unsloth-zoo (which depends on torch) in no-torch mode.

* fix: install unsloth + unsloth-zoo with --no-deps in no-torch mode

Instead of skipping unsloth-zoo entirely (which breaks unsloth's
dependency on it), install both packages with --no-deps so they are
present but torch is not pulled in transitively. Applied consistently
across all no-torch paths: migrated-env, fresh-local, fresh-non-local
in install.sh, install.ps1, and install_python_stack.py.

* chore: temporarily remove test files (will be added in a follow-up)

* refactor: deduplicate SKIP_TORCH conditional branches in installers

Collapse if/else blocks that differ only by --no-deps into a single
branch with a conditional flag variable. Applied to migrated-env and
fresh-local paths in install.sh, install.ps1, and install_python_stack.py.

* fix: apply --no-deps to fresh non-local --no-torch install path

The non-local else branch was missing $_no_deps_arg/$noDepsArg, so
uv pip install unsloth would resolve torch from PyPI metadata (the
published unsloth package still declares torch as a hard dep). Now
--no-deps is applied consistently to all SKIP_TORCH code paths.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

studio/install_python_stack.py

@@ -13,6 +13,7 @@ PATH to point at the venv.
 from __future__ import annotations
 
 import os
+import platform
 import shutil
 import subprocess
 import sys
@@ -21,6 +22,25 @@ import urllib.request
 from pathlib import Path
 
 IS_WINDOWS = sys.platform == "win32"
+IS_MACOS = sys.platform == "darwin"
+IS_MAC_INTEL = IS_MACOS and platform.machine() == "x86_64"
+
+
+def _infer_no_torch() -> bool:
+    """Determine whether to run in no-torch (GGUF-only) mode.
+
+    Checks UNSLOTH_NO_TORCH env var first.  When unset, falls back to
+    platform detection so that Intel Macs automatically use GGUF-only
+    mode even when invoked from ``unsloth studio update`` (which does
+    not inject the env var).
+    """
+    env = os.environ.get("UNSLOTH_NO_TORCH")
+    if env is not None:
+        return env.strip().lower() in ("1", "true")
+    return IS_MAC_INTEL
+
+
+NO_TORCH = _infer_no_torch()
 
 # -- Verbosity control ----------------------------------------------------------
 # By default the installer shows a minimal progress bar (one line, in-place).
@@ -161,6 +181,19 @@ def run(
 # Packages to skip on Windows (require special build steps)
 WINDOWS_SKIP_PACKAGES = {"open_spiel", "triton_kernels"}
 
+# Packages to skip when torch is unavailable (Intel Mac GGUF-only mode).
+# These packages either *are* torch extensions or have unconditional
+# ``Requires-Dist: torch`` in their published metadata, so installing
+# them would pull torch back into the environment.
+NO_TORCH_SKIP_PACKAGES = {
+    "torch-stoi",
+    "timm",
+    "torchcodec",
+    "torch-c-dlpack-ext",
+    "openai-whisper",
+    "transformers-cfg",
+}
+
 # -- uv bootstrap ------------------------------------------------------
 
 USE_UV = False  # Set by _bootstrap_uv() at the start of install_python_stack()
@@ -273,8 +306,13 @@ def pip_install(
         constraint_args = ["-c", str(CONSTRAINTS)]
 
     actual_req = req
+    temp_reqs: list[Path] = []
     if req is not None and IS_WINDOWS and WINDOWS_SKIP_PACKAGES:
         actual_req = _filter_requirements(req, WINDOWS_SKIP_PACKAGES)
+        temp_reqs.append(actual_req)
+    if actual_req is not None and NO_TORCH and NO_TORCH_SKIP_PACKAGES:
+        actual_req = _filter_requirements(actual_req, NO_TORCH_SKIP_PACKAGES)
+        temp_reqs.append(actual_req)
     req_args: list[str] = []
     if actual_req is not None:
         req_args = ["-r", str(actual_req)]
@@ -298,8 +336,8 @@ def pip_install(
         pip_cmd = _build_pip_cmd(args) + constraint_args + req_args
         run(f"{label} (pip)" if USE_UV else label, pip_cmd)
     finally:
-        if actual_req is not None and actual_req != req:
-            actual_req.unlink(missing_ok = True)
+        for temp_req in temp_reqs:
+            temp_req.unlink(missing_ok = True)
 
 
 def download_file(url: str, dest: Path) -> None:
@@ -352,6 +390,8 @@ def install_python_stack() -> int:
     # When --local is used, overlay a local repo checkout after updating deps
     local_repo = os.environ.get("STUDIO_LOCAL_REPO", "")
     base_total = 10 if IS_WINDOWS else 11
+    if IS_MACOS:
+        base_total -= 1  # triton step is skipped on macOS
     _TOTAL = (base_total - 1) if skip_base else base_total
 
     # 1. Try to use uv for faster installs (must happen before pip upgrade
@@ -399,6 +439,28 @@ def install_python_stack() -> int:
     # 3. Core packages: unsloth-zoo + unsloth (or custom package name)
     if skip_base:
         print(_green(f"✅ {package_name} already installed — skipping base packages"))
+    elif NO_TORCH:
+        # No-torch mode: install unsloth + unsloth-zoo without torch deps
+        _progress("base packages (no torch)")
+        pip_install(
+            "Updating base packages (no-torch mode)",
+            "--no-cache-dir",
+            "--no-deps",
+            "--upgrade-package",
+            "unsloth",
+            "--upgrade-package",
+            "unsloth-zoo",
+            req = REQ_ROOT / "base.txt",
+        )
+        if local_repo:
+            pip_install(
+                "Overlaying local repo (editable)",
+                "--no-cache-dir",
+                "--no-deps",
+                "-e",
+                local_repo,
+                constrain = False,
+            )
     elif local_repo:
         # Local dev install: update deps from base.txt, then overlay the
         # local checkout as an editable install (--no-deps so torch is
@@ -462,16 +524,22 @@ def install_python_stack() -> int:
     )
 
     # 4. Overrides (torchao, transformers) -- force-reinstall
-    _progress("dependency overrides")
-    pip_install(
-        "Installing dependency overrides",
-        "--force-reinstall",
-        "--no-cache-dir",
-        req = REQ_ROOT / "overrides.txt",
-    )
+    #    Skip entirely when torch is unavailable (e.g. Intel Mac GGUF-only mode)
+    #    because overrides.txt contains torchao which requires torch.
+    if NO_TORCH:
+        _progress("dependency overrides (skipped, no torch)")
+    else:
+        _progress("dependency overrides")
+        pip_install(
+            "Installing dependency overrides",
+            "--force-reinstall",
+            "--no-cache-dir",
+            req = REQ_ROOT / "overrides.txt",
+        )
 
     # 5. Triton kernels (no-deps, from source)
-    if not IS_WINDOWS:
+    #    Skip on Windows (no support) and macOS (no support).
+    if not IS_WINDOWS and not IS_MACOS:
         _progress("triton kernels")
         pip_install(
             "Installing triton kernels",